Deformation of tissues is commonly performed during surgery or other medical procedures either to achieve surgical access or to specifically alter the dimensions of one part of the anatomy. Examples of deformations of tissue for surgical access include spreading ribs during a thoracotomy, spreading a bisected sternum during a sternotomy, and separating the vertebrae of the spine for surgery on the intervertebral disk. Examples of deformation of tissues to alter the dimensions of the tissue include angioplasty to open blocked arteries, valvuloplasty to enlarge heart valves, and distraction to adjust the position of vertebrae. Such deformations are collectively referred to herein as “retraction”.
Spreaders, retractors, distractors, and even angioplasty balloons (collectively called “retractors” here) can impose significant forces on the surrounding tissues during retraction. The resulting strain on these tissues, and on associated tissues such as the ligaments attaching ribs to vertebrae, can be large, leading to damage of these tissues, including the fracture of ribs and the rupture or irreversible deformation of ligaments and other fibrous tissues.
Retraction occurs in two different phases—deforming the tissue (referred to herein as the first phase or retraction) and holding the tissue at that deformation (referred to herein as the second phase of retraction). Usually both are done with the same instrument. For example, a rib spreader is used both to force the ribs apart during a thoracotomy and to hold the ribs apart during the surgical procedure. Sometimes two different instruments are used, especially if the deformation is to be permanent. For example, an angioplasty balloon is used to force open an atherosclerotic plaque, and then a stent is used to hold the artery open; or a distractor is used to separate vertebrae, and a metal plate is used to secure the vertebrae in that position. An example of two different instruments being used when the deformation is not permanent is disclosed in U.S. Pat. No. 5,201,325 by McEwen (McEwen, Auchinleck et al. 1993), therein a surgeon manually retract an incision with a disclosed retractor blade, and an automated mechanism is then used to hold the incision open. In the medical literature, both phases are frequently referred to as retraction.
Both phases of retraction traumatize tissue. Trauma from the first phase of retraction can include the rending and tearing of tissues—bones bend and break; muscles stretch beyond normal limits; ligaments and other connective tissues stretch and tear; or nerves are stretched. Trauma from the second phase of retraction can include ischemia of the tissue due to elevated tissue pressure, for example, under a retractor blade; blockage of nerves; and blockage of blood vessels causing ischemia in tissues distant from retraction.
Tissue trauma and ensuing complications resulting from retraction can be greater than the trauma resulting from the medical procedure that required the retraction. For example, thoracotomies are extremely traumatic, and can result in post-surgical pain and respiratory complications that exceed that of the thoracic procedure, such as a lung segmentectomy.
There is, therefore, need for improved methods and devices to perform one or both phases of retraction.